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Baseline Parameters and Layout 1
Rev. May 8, 2006

Baseline Parameters and Layout 2
1.1
Layout of the ILC Accelerator Complex
1.1.1
Overview
Figure 1 shows a schematic view of the baseline layout for ILC (OCT 6, 2006) in its phase-1 configuration which supports physics experiments at center-of-mass energies up to 500 GeV. The site footprint is dominated by two main linacs, for accelerating electrons and positrons, respectively, each of which extends over a length of approximately 10 km.
Together with the electron sources, damping rings and the beam delivery systems, the total site length is expected to be approximately 31 km.
REPLACE with OCT 6 LAYOUT……………………attached file
Figure 1: Schematic view of the ILC baseline layout for phase-1.
1.1.2
Electron Source
The electron source is the point of origin of all ILC beams in normal operation. The positron beam in normal operation will be generated by photons produced by the passage of electron beams through the undulators. The electron source will be part of the Central
Injector/Damping Ring complex (see fig.1). It is located on the e+ linac side of the the
Damping Ring which has an electron and a positron ring in the same tunnel. The exact location of the electron source will be determined through optimization of the injection beam line into the damping ring. The polarized electron source system includes one 5GeV linac to inject the beam into the electron damping ring.
1.1.3
Damping Rings
The damping rings, operated at the beam energy of 5 GeV, will reduce the beam emittance to the level required by the specifications discussed in Section 1.1. The rings are approximately 6.7 km in circumference. The baseline layout has the damping rings located centrally between the linacs and above the level of the beam delivery system. The elevation difference will give adequate sheilding to allow operation of the INJ/DR complex with other ILC systems in open access. One electron and one positron ring in the same tunnel are assumed in this baseline configuration. The exact locations of the damping rings may be site-dependent. It is noted that simple longitudinal (parallel to the main linacs) relocation of the damping rings does not affect the timing constraint since what needs to be preserved is the relation between the circumference of the damping ring and the path length of the round trip from the undulator souce point of the complex to the operating interaction point.However, other changes to the layout of ILC systems, such as relocation of the damping rings transverse to the main linacs, the lengths of the linacs or
Rev. May 8, 2006

Baseline Parameters and Layout 3 the beam delivery systems will change timing requirements and solutions.
1.1.4
Ring-to-Main-Linac
The RTML beam line begins at the damping ring and transports the damped beam through the linac tunnel to the low energy end where it turns through 180 degrees. The RTML includes a suitable set of beam diagnostics, bunch compression and spin manipulation sections. The 180˚ turn-around,. allows the application of a feed-forward beam stabilization system. After the turn-around, in the bunch compressor, the beam is accelerated up to 13-15 GeV before injection into the main linacs. These 10 km, 5 GeV beam transport lines from the central complex to the beginning of the linacs are required to maintain the low emittance of the damped beams. They are therefore more complex in instrumentation and correction than the e+ transport lines that they replace in the previous
ILC layouts. However these issues have been studied and considered in changing to a central INJ/DR complex.
1.1.5
Main Linacs
The main linacs receive the beams from the RTML at 13-15 GeV and accelerate them up to 250 GeV in normal phase-1 operation. As discussed below, the main linacs on the electron side are interlaced by undulators to incorporate the positron production system, or segments associated with beam diagnostics, and tune-up dumps for ensuring good operability.
The angle between the two main linacs is irrelevant to the design of most collider systems.
An exception is that the Beam Delivery System requires this value for detailed optics design. The present baseline design has two beam delivery transport lines leading to two interaction points where the beams interact with a 14 mrad crossing angle.
1.1.6
Positron Source
Positrons in normal operation are produced with photons originating from the electron beam from the main linac at an energy of 150 GeV. For that purpose a 200 m-long undulator system is incorporated in the electron main linac. The positron production target that converts these undulator photons to positrons is located on the “electron side” of the
IR. After acceleration up to 400 MeV, the positron beam is brought to the central INJ/DR complex and accelerated to 5 GeV by a pre-accelerator before injection into the positron damping ring. The trajectory of the positrons upon extraction from the positron damping ring is essentially a mirror image of that of the electrons.
To allow commissioning or debugging of the positron damping rings, positron RTML and the positron main linac, an auxiliary (or keep alive) positron source will be provided at the entrance to the 5 GeV positron pre-accelerator.
1.1.7
Beam Delivery
The beam delivery system receives the beams of energies up to 250 GeV in phase-1 operation, collimates them, focuses them, collides them at the interaction points, and
Rev. May 8, 2006

Baseline Parameters and Layout 4 safely disposes of the exhaust beam at the beam dumps. In the baseline layout, the ILC supports two interaction regions which provide collisions at beam crossing angles of 14 mrad..
1.1.8
Elevation Layout
In the baseline configuration, the bulk of the main linacs will be built approximately following the “local horizontal” lines that are defined by the local gravity in its neighborhood. This is the preferred elevation layout from the standpoint of straightforward engineering implementation of the liquid He leveling within the main linac cryostats.
However, for sake of ensuring emittance controls and beam tuning, the entire beam delivery system beam line is to be built to stay in a single mathematical plane normal to the gravity vector at a point near the interaction regions. The INJ/DR complex will also be on the same plane with an elevation difference of 10 to 20 meters.
1.1.9
Path Length Constraints
The fact that positrons are produced by undulator photons which are produced by electrons within previous machine pulses lead to special issues of timing controls. They lead to constraints or preferences on various aspects of the ILC design, including the choice of the circumference of the damping rings and all the beam line path lengths.
A detailed analysis of this issue has been reported by A.Wolski et al in [2]. It is understood that an integral relationship is highly desired between the circumference of e+ damping ring and the path length a new positron bunch travels in a round trip through the INJ/DR complex, the RTML, the main linac and the beam delivery.
The baseline solution for these issues was the insertion of 1.2 km into the positron linac comparable to the positron production region in the electron linac. This insert would contain a few hundred meter path length adjuster which is no longer required as the interaction regions and detectors are now at the same longitudinal location. The whole 1.2 km insert in the e+ linac has been removed and the “Keep alive source” is now part of the central complex. See 1.2.6. The positrons now pass through an additional half turn in the damping ring between injection and extraction and this partially corrects the e+/- timing.
Further correction will be required but the amount is dependent on the lengths of so many systems which are presently under review, that a decision on the optimum correction methodology will be delayed until some time in the future. There are many possible timing correction strategies which will be considered at this time.and compared with the cost of a
1 km insert in e+ linac.
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1.1.10
Hardware Layout within the Tunnels
Following the study presented in the Section 12.3 “Number of Tunnels” of GDE White
Papers ( http://www.linearcollider.org/wiki/doku.php?id=bcd:bcd_home ), the hardware for
Rev. May 8, 2006

Baseline Parameters and Layout 5 the main linacs (and many of other subsystems) will be implemented in two parallelrunning tunnels. More discussions are found in the “Conventional Facilities and Siting” section of BCD.
1.1.11
Energy Upgrade and the Accelerator Layout
The first phase (500 GeV centre-of-mass) will be constructed using a tunnel long enough to support a gradient of 31.5 MV/m operational gradient (~2×10 km assuming a 0.75 fill factor). A second phase (phase 2) upgrade to 1 TeV centre-of-mass will then require extending the tunnel (away from the IR) an additional ~2×9.3km assuming cavities capable of 36 MV/m operational gradient.
The Beam Delivery System will be configured so that it can support operation at 1TeV with only minor upgrades. The main dump systems will be configured for the 1 TeV option from the start.
Injectors will be configured for phase 1 so that there is a minimum impact on them when upgrading to phase 2. Prospective sites must be chosen with the TeV phase 2 machine in mind; specifically the availability of both the total required land and power.
References
[1] http://www-project.slac.stanford.edu/ilc/acceldev/beamparameters.html
, http://www-project.slac.stanford.edu/ilc/acceldev/beampar/Suggested ILC Prameter
Space.pdf
[2] “Recommendations for ILC Configuration Satisfying Timing Constraints,” by
H.Eh
r lichmann, S.Guiducci, K.Kubo, M.Kuriki and A.Wolski, submitted to GDE
Executive Committee on April 7, 2006. Available from: http://www.linearcollider.org/wiki/lib/exe/fetch.php?cache&media=bcd:timingrecom mendations-revapril17.pdf
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Rev. May 8, 2006